This invention relates to a hydrogen generator with a pump for pumping liquid reactant, and to a fuel cell system including the hydrogen generator.
Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
There are several types of fuel cells, which can be classified in various ways. For example fuel cells can be categorized according to the type of electrolyte used, typically one of five types: proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC). Each of these types of fuel cell uses hydrogen and oxygen. Hydrogen is oxidized at the negative electrode, and oxygen is reduced at the positive electrode. Ions pass through an electrically nonconductive, ion permeable separator and electrons pass through an external circuit to provide an electric current.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (a fuel cell stack), and a gas source, such as a gas tank or a gas generator. Gas generators that supply gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable gas generator can be replaced with another one when the gas producing reactants have been consumed. Removable gas generators can be disposable (intended for only a one-time use) or refillable (intended for use multiple times) to replace consumed reactant materials.
It is desirable for removable gas generators to be easily coupled to the fuel cell system to create a gas flow path from the gas generator to the remainder of the fuel cell system without gas leaks at the coupling, and it is also desirable for the gas generator to be free of gas leaks when not coupled to the remainder of the fuel cell system. The coupling between the gas generator and the rest of the fuel cell system can include one or more valves. The valve(s) can be opened and closed manually, valve operation can be controlled by a control system, or the valve(s) can be opened and closed by an actuator that is operated by making or separating components of the coupling. The latter method can be used in quick disconnect couplings, for example, where the valve is opened when the gas generator is coupled to the rest of the system and closed when the gas generator is uncoupled.
Gas generators can use a variety of types of reactants to produce the gas. In one type of hydrogen generator, at least one reactant is stored in a reservoir as a liquid, and the liquid is transferred from the reservoir to a reaction chamber, where it reacts to produce the desired gas. Various means have been used to transfer the liquid, including gravitational flow, application of pressure to the liquid, wicking the liquid by capillary action, and pumping with a mechanical pump. Each method has advantages and disadvantages.
Pumping the liquid can be advantageous because the pumping can be started and stopped, so gas is produced on an as-needed basis. A pump can also provide the liquid at a controlled rate. In selecting a pump to be used with a gas generator, many factors can be considered, such as compatibility of the pump materials and components with the liquid being pumped, the ability of the pump to withstand the environment in which it is to be used (e.g., temperature and pressure), the size of the pump, the pumping rate, rate control (accuracy and precision), the amount and type of power required to operate the pump, integration of the pump into the gas generator or the system, compatibility of the pump with the method of controlling the production of gas, the reliability of the pump, and the amount of heat and noise produced by the pump during operation.
In view of the above, an object of the present invention is to provide a pump that is suitable for pumping liquid reactant in a gas generator and a fuel cell system including the pump, particularly a fuel cell system that can be used to power portable consumer electronic devices such as communications equipment, portable computers and video games.